As part of an NIMH-supported study of schizophrenia, a group of 5,483 adoptees born in Denmark between 1924 and 1947 was identified. Names of their biological parents were obtained and psychiatric registries searched to determine who had been admitted to a psychiatric facility. Information about the adoptees and parents was made available to the present investigators who identified a group of parents who had received a hospital diagnosis of alcoholism. Their male offspring, adopted early in life to foster parents, were interviewed and it was found they had significantly more alcohol problems than did a control group of adoptees without an alcoholic biological parent. The adoptees' siblings who were raised by the alcoholic biological parents were subsequently studied and found to have an alcoholism rate not significantly different from their adopted brothers (17 vs. 25%). The overall objectives of the study is to identify and separate genetic and environmental factors as they interact to produce alcoholism, utilizing the unique opportunity the Danish adoptive cohort provides for separating these factors.